Semiconductor component manufacturers are constantly striving to increase the speeds of their components. Because a semiconductor component, such as a microprocessor, contains up to a billion transistors or devices, the focus for increasing speed has been to decrease gate delays of the semiconductor devices that make up the semiconductor component. As a result, the gate delays have been decreased to the point that speed is now primarily limited by the propagation delay of the metallization system used to interconnect the semiconductor devices with each other and with elements external to the semiconductor component. Metallization systems are typically comprised of a plurality of interconnect layers vertically separated from each other by a dielectric material and electrically coupled to each other by metal-filled vias or conductive plugs. Each layer contains metal lines, metal-filled vias, or combinations thereof separated by an insulating material. Typically, the metallization system is coupled to the semiconductor substrate through a metal contact.
A figure of merit describing the delay of the metallization system is its Resistance-Capacitance (RC) delay. The RC delay can be derived from the resistance of the metal layer and the associated capacitance within and between different layers of metal in the metallization system. Included in the resistance component of the metallization system is the contact resistance between the metal contact and the semiconductor substrate. The metal may directly contact the semiconductor substrate or it may be coupled to the semiconductor substrate through a metal silicide layer. Many types of metal can be used for the contact. Typical metals include titanium, tantalum, tungsten, cobalt, nickel, copper, aluminum, or the like. When the metal is tungsten, a titanium liner is formed on the semiconductor substrate or the silicide, a titanium nitride barrier layer is formed over the titanium liner, and tungsten is formed on the titanium nitride layer. The titanium liner lowers the contact resistance between the semiconductor substrate and the tungsten. The titanium nitride barrier layer prevents fluorine that is used in the tungsten deposition process from attacking the semiconductor material and forming pits in it. Pit formation is undesirable because tungsten becomes deposited in these pits, thereby increasing the contact resistance. These tungsten-filled pits are referred to as wormholes. In a conventional tungsten contact process, the tungsten is not conformally deposited. Thus, tungsten seams or gaps are formed in small tungsten contacts which increase the contact resistance. Another drawback with the conventional tungsten contact process is that the titanium liner and titanium nitride barrier layers involve sophisticated processing steps with low throughputs, which increase the cost of manufacturing the semiconductor component.
Accordingly, it would be advantageous to have a method for manufacturing a tungsten contact that inhibits wormhole formation. It would be of further advantage for the method to be cost and time efficient.